The present invention relates to a torque gauge, and more particularly to a gauge using magnetoelastic properties of materials for sensing torque particularly experienced by the mechanical hand of a robot.
It is well known that various magnetic properties of magnetic materials changed due to applied stress. In particular, the permeability of the magnetic material tends to increase due to tensile stress and tends to decrease due to compressive stress. Thus, stress can be measured taking advantage of ferromagnetic substances exhibiting this property.
Electrical signals can be converted into a mechanical displacement or the reverse, using the magnetostrictive effect by placing a magnetostrictive material in a magnetic field, i.e., a change in the physical dimensions of the magnetostrictive material causes a change in the magnetic state of the magnetostrictive material. This is called the Villari effect.
In general, a good magnetostrictive material has high electrical resistivity, low magnetic anisotropy, large magnetization, and large isotropic magnetostriction. All crystalline materials have some magnetic anisotropy as well as magnetostriction which is not perfectly isotropic. The largest room temperature magnetostrictive strains are exhibited by rare earth-iron intermetallic compounds. However, these and similar alloys also have the problem that the magnetostrictive effect is very anistrophic with large strains occurring along the (III) direction and very small ones along the (I00) direction. To produce a large magnetostrictive effect in such an alloy with very low applied magnetic fields requires using either a single crystal or a highly texture polycrystalline sample. Generally, alloys which do not contain rare earth elements have much smaller magnetostrictive strains and must employ special combinations of rare earths to reduce magnetic and isotrophy.
Amorphous magnetic alloys inherently have low isotrophy and thus are well suited for such an application. Amorphous magnetic alloys can be prepared by several methods, among the easiest are coevaporation or sputtering onto cold substrates. Usually some method involving rapid quenching of the melt is necessary.
Towards this end, amphorous ribbons recently developed are particularly applicable to exhibit the Villari effect. The permeability of the material to be measured varies in dependence on the strain of the material to be measured. Accordingly, the variation of the permeability of the material to be measured can be detected as the variation of magnetic flux density upon application of a magnetic field to the material to be measured. The magnetic material can be made from a magnetic material which is manufactured by quenching from a liquid phase and then formed as a thin sheet. The materials magnetically exhibit ferromagnetism and have a high level of magnetic saturation, high permeability of greater than 10.sup.3 and a low level of coercive force, less than 1.0 (Oe) while mechanically exhibit a high break strength, excellent resiliency and stability, and have small changes of magnetic characteristic under temperature variations.
With an applied magnetic field, the change in permeability in a magnetic layer on the surface is sensed by one or more pick-up coils located adjacent to the magnetic material. The inductance of the coil is directly proportional to the permeability of the core, the square of the radius of the coil, and inversely proportional to the length of the coil. Thus, for a given pick-up coil, the inductance of the coil is directly proportional to the permeability of the core material located within the coil. Since the permeability of a magnetic material chosen is directly proportional to the stress applied to the material, the inductance of a coil surrounding a magnetic material is directly proportional to the stress applied to the magnetic material coil. The inductance of the pick-up coils is determined by means of an electronic processor coupled to the coils. This structure provides for the sensing of small amounts of torque in a small and rugged configuration.
There is a increasing need for work to be done by automation. With robots being used in increasing numbers for assembly line work and in hazardous working environments such as with explosives, radioactive materials, and chemical processes, it is necessary for the robot to be provided with tactile sensing.
Accordingly, it is desirable to provide a torque measuring apparatus which is very sensitive to small amounts of torque and for that measuring apparatus to be providable in a small and rugged configuration which can be utilized in the hand of a robot.